Tangentially finned heat exchange tube



May 4, 1954 A. HUET TANGENTIALLY FINNED HEAT EXCHANGE TUBE Filed April 6, 1950 IN VEN TOR.

ANDRE #05 T .4 Tr m Er Patented May 4, 1954 TANGE'NTIALLY FINNEDIIEAT EXCHANGE" TUBE Andr Huet, Paris France.

Application April6,'1950;'SerlaliNb. 154 213 1 Claim.

This invention relates to heat-exchangers and particularly to an improved form and-arrangement of tubes provided with integral longitudinal fins'as extended surface.

Inan earlier application, Serial No.. 748,561,

filed May 16, 194:7, now Patent No. 2,578,136 dated December 11, 1951; of which this is acontinuationin part, applicant has described finned heat exchange tubes each provided with two longitudinally" disposed fins locatedapproximately diametrically opposite each other with the planes of the-fins being tangent to the surface of the tube which is swept by the exterior fluid flowing inla direction perpendicular to theaxis'of the tubes.

One of the advantages resulting from. this arrangement is that when an exchanger has a bundle of such tubes. disposed in staggered relation, there are formed between .the tiers'of tubes sinuous channels of variable sectionwhoseboun daries are determined by the fins and the surfaces of the tubes. The exterior fluidflows in these sinuous channels which, because-of the disposition adopted for the fins andtubes, present restrictions and enlarged parts, thesevariations of section assuring variations of pressure-and of" speed in the flow of exterior-fluid, as well as:

changes in directions of flow, which contributed favorably to the efficiency of the'heat exchanger. As a result of tests andexperience with-heat exchangers provided with tangentially finned tubes of the type described above, it has been discovered that it is possible to further increase theprovided with specially shaped tangential fins which on adjacent tubes cooperate to present channels having successive restrictions and/or changes of direction followedby gradual enlargements of the section providedfor the passage of the fluid. These are in the generalform ofa divergent up to the next restriction or change of direction of the passage afforded for the flow of fluid.

When the exchanger is made up of a bundle of parallel tubes disposed in staggered relation and provided with tangential fins as mentioned above, the tangential fins which define-part of the boundaries of'thechannels that-arebffered totheflow of the exteriorzfluidsarezsuitablyjchick -vergent that fellowsthe restriction etc.

to-the-maintenanceof this favorable flow along 2 enedand profil'ed'or shaped insuch fashion that i1r=combination=witli the staggered disposition of the-tubes'tliechannelsection afforded for the new oi exterior"fluidfenlarges gradually from one restrictionof a channeI tothe following restriction.

The increase ofefilcienoy-obtained by the arrangement outlined above results from the following considerations: when a fluid circulates at a certain-speedin' a passage of constant section, the laminar fl'owof the fluid changes at tiieend'of a certain' distance of travel into a turbulent flow which provokes cavitations while a film 'offiuid remains adherent to the boundaries oith'epassage: Inthe case of a heatexchanger tube bundle'where the exchange of heat is between two fluids= flowingrespectively exteriorly of the tubes an'd' within them such a fluid film on the external surface of the tubes has the efiect, since itis notrephced by fresh fluid, of diminishing the exchange of heat'and, consequently, de-

creasing th'e'efiicien'cyof the heat exchanger. On

the'otherhan'd the cavitations and turbulence increase the draft -loss in the exchanger.

When in accordancewith the invention, the

channels'traversed by the exterior fluid present successive restrictions followed by progressive dilations-of the sectionsof achannel formed between two slightlydivergent boundary surfaces -there-ismaintainedamodeof fluid flow at relatively high rates of flow that eliminates the for mation of turbulence throughout the entire length of 'tlie fluid passage.-

Ineffect; the -restriction of section presented to the-flow of the fl'u-ids' produces, at the moment when the flcw-"wouldtend to become turbulent, a reaction which assures the maintenance of proper flowfor'the efficient "exchange of heat which it againattainsthroughoutthelength of the di- Thanks the'whole-lengthof the fluid passage, the fluid film incontact with the boundaries is diminished and constantly renewed without producing sub stantial cavitations or turbulence and the renewal oi-thisfilmof 'fiuid assuresin the caseof a--heat=exchangenan increase of efliciency since theiexch'ange of" heat can then be effected more easily between fiuidsfldwing from one part to another 'of theboundary.

The figureshowsin' section a portion of a tube bank in" a' heat exchanger' having tangentially finne dh'eat exchange tubes in accordance with thepresent inventions The" tubes's-fi I0:1'are arranged in parallel rows surface.

whose axes, such as XX, YY, Z-Z in the figure, are shown as inclined across the gas stream at an angle to the general direction of flow through the passage as indicated by the arrows A. Each tube ill is provided with two flat longitudinally extending fins 2B and 2| welded at 180 with respect to each other on the periphery of the tube and projecting in directions approximately tangential to the surface of the tube. One side face if of each fin 2E, 2| is flat or planar and substantially tangential to the tube while the opposite face If is concavely curved from the distal end [3 of the fin to its junction 254 with the tube, at which point it is substantially tangential; i. e. the arc of its surface and that of the tube meet on a tangent. The finned tubes are more or less symmetrical since the downstream fins 2| while similarly profiled are disposed with their curved and planar surfaces oppositely arranged to those of the upstream fins 20. As shown in the drawing the tubes ID are arranged at equal intervals in staggered relation in uniformly spaced parallel rows and disposed in such fashion in the gas passage that the fins 23, iii are on the upstream and downstream faces of the tubes and slightly inclined with respect to the general direction of the heating gas current which follows the direction of the arrow A. This inclination could be eliminated and the fins 29, 2| located parallel to the direction of gas flow which is indicated by arrow A.

With the arrangement described above, the main fluid stream flowing in the direction of arrow. A is split up by the upstream fin 20 so that the left hand current comes into contact with the tube it as indicated by the arrow B (lower right in the figure) and wipes against about 120 of its At the moment, when conforming to conventional aero-dyna1nic theories, the stream should begin to flow around the back face 22 of tube Hi and create a void with eddy currents, it has reached the base of the fin 2| which it sweeps over on the left hand face HA in the direction of the arrow C. On the right hand face I of the upstream fin 2c the fluid current which follows the arrow D wipes against about 120 on the right hand face of the tube Ill and in following the arrow E curves against the back of the tube and is finally turned away by the right hand face |2A of the downstream fin 2| so as to follow the arrow F.

It may be seen that with this arrangement the entire surface of a tube l0 and its fins 20, 2| is secured by the currents of hot gases and consequently an optimum heat exchange is assured.

From one row to another of tubes in the heat exchanger the fins can be disposed parallel in similar fashion or can be alternated so that upstream fins are first on the right, then the left etc. With the tubes spaced at like distances in each row and the fins in corresponding locations on the tubes, the upstream fin on tubes of one row aline with and are in approximate contact with the downstream fins 2| in a following row. The distal ends 13 of the fins may be close together or actually in contact to form separated gas lanes. The fins on tubes in adjacent rows may be in approximate contact at a point in a plane T parallel to the general direction of flow and passing through or close to the axis of the tube. The arrangement shown places the tube bodies in the intermediate rows opposite the distal ends of fins on tubes in the immediately following and preceding rows. This narrows the gas lanes at H and widens them at N. Thus,

the entire width of the heat exchange pass is divided into a number of sinuous channels made up of alternately narrowing parts H followed by widened parts N in continuous series through the bank. In passing through the narrow sections H the velocity of the stream increases and then upon expanding in the widened sections N the energy obtainable is converted from velocity to ,static pressure so that the streams completely fill the channel spaces between the tubes and the heating gas flows in intimate contact with the tubes and their fins to assure the most eificacious heat transmission between the gas and the fluid flowing through the interior of the tubes l0.

As is seen, these channels between tiers of tubes are of varied section and present restrictions H and/or changes in direction located for example at the height of the plane passing through the axis of the two tubes MA, MB (lowor right) corresponding in neighboring tiers. According to the invention the surface of the tangential fins are such that beginning with one restriction H and continuing to near the restriction H located downstream therefrom the channel affords to the fluid A a gradual divergent between the boundary lines GK on one side and LP on the other side. To give to the channel part located beyond each restriction H this divergent boundary GK, LP the tangential fins mounted on the upstream and downstream sides of the tubes have different profiles, the lower fins 2| for example, being slightly thicker than the upper fins 20.

The downstream fin 2| on a tube is stated as being thicker than the upstream fin 2t hence while the fins are mounted at diametrically spaced points on the tubes the increased thickness of the lower fins 2| at the point of juncture with the tube causes the planar portion ||A of the downstream fin 2| that is included in the boundary surface GK to diverge slightly from parallelism with the confronting flat surface ll of the tangential fin on the top or upstream side of the tube in the adjacent row thereby gradually increasing the section of the passage from a point where the downstream fin 2| is tangent to the tube to a point where the distal end of the fin is in substantial alinement with the edge of the upstream fin 20 on the tube below.

What I claim is:

In a heat exchanger having a passage through which gases flow over tubes spaced in parallel rows located in planes perpendicular to the gas flow with the tubes in adjacent rows staggered and dividing said passage into a number of sinuous gas lanes; longitudinally extending fins on the upstream and downstream sides of the tubes each having a planar face tangential to its tube with the other face of each fin concavely curved from its distal end to its junction with the tube at a point where said curved face becomes sub stantially tangential, the downstream on each tube being tangential thereto at a point slightly more than from the planar face of the upstream fin and its other face being curved on a greater radius than that of the upper fin with the faces of the downstream fin disposed reverse 1y to those of the upstream fin so that planar faces of fins on tubes in one row confront planar faces of fins on the tubes in rows upstream and downstream thereof out of parallelism therewith and bound sections of the gas lanes that are gradually enlarged in the direction of flow while the curved face of a fin confronts tube surfaces opposite and between the two fins on a tube in an adjacent row, the distal edge of the planar face of the downstream fin on each tube being substantially in alinement with the corresponding distal edge of the curved face of the upstream fin on a tube therebeyond substantially in a plane lying parallel to the general direction of flow and passing substantially through the axis of said adjacent tubes and the said downstream fins being thicker at their distal ends than the upstream fins and tapering to their roots at the tube surfaces so that gas lanes opposite the curved faces of said downstream fins are narrower than lanes bounded by the more sharply curved faces of upstream fins.

References Cited in the file of this patent UNITED STATES PATENTS Number Number 

